If the things run off 5v or 12v it should be straightforward. Those are the two voltages provided in the standard connector used for drives and stuff. Just to connect them backwards, or else you'll toast something.

You don't connect the wall plug, but get a connector that fits the DC input on the device, where the wall-wart cord comes in. Then you get a 4-pin molex connector and a wire, and connect the relevant voltage and ground on the molex and the DC input on your device. It means replacing the included power adapter with your computer PSU.

Sure it's doable! Whether or not you survive the experiment remains to be seen, though... No really, what I would do is this:

kevinfelker42 wrote:

OK, so there would be actual wire stripping and binding involved.

#0) Do not kill or injure yourself! If you're unsure of these things, don't mess with them.

#1) Examine each of your devices power label, wall-wart or brick supply and check its label: does it run on 5 or 12 volts? If yes, then it's easy to come by from your PSU. 7V can be managed as well, if tricky.

#2) Grab a kill-a-watt and measure the power draw of each device (using its stock power plug) to see if your PSU will be able to drive them. This is also determined by the rating of your PSU and the rest of the components in the pc.#2a) My guess is, if all you want to run are desktop speakers and a home router, then yes there's no problem. #2b) If you want to power a printer or separate laptop, too, that would probably be problematic, both in terms of odd voltages (not 5 or 12) and power draw (wattage).

#3) (For each device:)#3a If you want to keep the stock power supplies intact: Buy appropriate cable and a matching power plug (the little one that goes into the device, not the wall plug).#3b) If you are sure you won't be using the wall-warts: snip the power cable close to the brick to re-use as much cable as required.

#4) Pay attention to the polarity!

#5) Buy Molex (12V) Y-cables (easiest) or plugs and make your own (harder), and splice your devices in. It's probably best to have one Y-cable for each external device, though it will make a cable mess. Are you sure it'll be worth it?

#6) Plug in one device at a time, stick your fingers in your ears, close your eyes, and hit the power switch with a toe.

#7) Watch the fireworks, or smile at your success.

morglum wrote:

since all these 12V devices are quite far from my computer

Well, you should not snake a 5V cable across a room, let alone an entire flat. These things need to be close together (as you would a display or an external drive).

Sure it's doable! Whether or not you survive the experiment remains to be seen, though... No really, what I would do is this:

kevinfelker42 wrote:

OK, so there would be actual wire stripping and binding involved.

#0) Do not kill or injure yourself! If you're unsure of these things, don't mess with them.

#1) Examine each of your devices power label, wall-wart or brick supply and check its label: does it run on 5 or 12 volts? If yes, then it's easy to come by from your PSU. 7V can be managed as well, if tricky.

#2) Grab a kill-a-watt and measure the power draw of each device (using its stock power plug) to see if your PSU will be able to drive them. This is also determined by the rating of your PSU and the rest of the components in the pc.#2a) My guess is, if all you want to run are desktop speakers and a home router, then yes there's no problem. #2b) If you want to power a printer or separate laptop, too, that would probably be problematic, both in terms of odd voltages (not 5 or 12) and power draw (wattage).

#3) (For each device:)#3a If you want to keep the stock power supplies intact: Buy appropriate cable and a matching power plug (the little one that goes into the device, not the wall plug).#3b) If you are sure you won't be using the wall-warts: snip the power cable close to the brick to re-use as much cable as required.

#4) Pay attention to the polarity!

#5) Buy Molex (12V) Y-cables (easiest) or plugs and make your own (harder), and splice your devices in. It's probably best to have one Y-cable for each external device, though it will make a cable mess. Are you sure it'll be worth it?

#6) Plug in one device at a time, stick your fingers in your ears, close your eyes, and hit the power switch with a toe.

#7) Watch the fireworks, or smile at your success.

morglum wrote:

since all these 12V devices are quite far from my computer

Well, you should not snake a 5V cable across a room, let alone an entire flat. These things need to be close together (as you would a display or an external drive).

Thansk for the how-to guide, very appreciated.

Messing with wires for hours isnt an issue for me. The "is it worth it" question is still up in the air :

What is the typical efficiency of a wall wart? If it's 35% vs my PSU's 80% then the 15W (made up number) my router needs would now require 18.75W instead of 42W.

A 23.25 W saving per device multiplied to my router, modem, nas and speakers would be great!

However if i'm only going from 60% to 80% then I doubt I'll do it.

Last edited by morglum on Thu Dec 11, 2008 12:31 pm, edited 1 time in total.

I can't say. It's a bit difficult to do, but you can actually get the efficiency for your wall wart. First you read the power draw as described above; then you need to place the kill-a-watt between the wart and the device, that is, route the wart's output through the meter; and finally compare the two readings to see how much power goes only to heat the wart instead of powering the device. You will need to cut the cable to do that, though, and your meter needs to be able to deal with not-just-110/220V supplies ... but really most meters do that, so it's just a matter of whether or not you want to hack the cables for this. Plus, on this side of the wart, there's no real danger of killing yourself.

Oh, and if you find out the efficiency of a couple of devices, post your findings!

I can't say. It's a bit difficult to do, but you can actually get the efficiency for your wall wart. First you read the power draw as described above; then you need to place the kill-a-watt between the wart and the device, that is, route the wart's output through the meter; and finally compare the two readings to see how much power goes only to heat the wart instead of powering the device. You will need to cut the cable to do that, though, and your meter needs to be able to deal with not-just-110/220V supplies ... but really most meters do that, so it's just a matter of whether or not you want to hack the cables for this. Plus, on this side of the wart, there's no real danger of killing yourself.

Oh, and if you find out the efficiency of a couple of devices, post your findings!

I've got a spare RP31P2 that will be going under the scalpel...

Basically :
wart input wattage : use kill-a-watt to get wattage
wart output wattage : measure ohmage going from the wart to the device by putting a multimeter there and multiply by the voltage to get the wattage.

How is the international efficiency marking protocol being implemented?The nameplate (or an equally visible location) of single voltage external ac-dc and ac-ac power supplies must be clearly and permanently marked with a Roman numeral from the sequence I (least efficient) to VI (most efficient) that corresponds to specific minimum Active and No-Load efficiency levels (as well as a power factor requirement for level V). The performance requirements for each Roman numeral are shown in the table below.To determine the appropriate Roman numeral, manufacturers: 1) compare the unitâ€™s Active, No-Load, and power factor test data (when tested in accordance with the ENERGY STAR Test Method and at each relevant test voltage and frequency value) with the performance requirements at each level of the Roman numeral scale; and 2) choose the highest Roman numeral where the power supply meets the Active, No-Load, and power factor (where applicable) requirements.

It seems that the main difference between level 3 and 4 is the "no load power".. which is .75W in level 3 and .5W in level4.

According to this, a 10W (2A * 5V) level IV power supply would have an efficiency of at least 0.74% -- hardly worth chopping.

At 74% efficiency and 0.5W idle power I doubt it's worth plugging to my psu.

*******
I just discovered (using my kill-a-watt) that my computer uses 6W even when completely shut down (WTF?!)

Yeah, that's the main reason I freecycled my lovely little Antec Aria -- the PSU drew 20W when connected only to the wall -- and not even a motherboard! That had to go. It's little comfort that it idled at like 38W and maxed out at 60, since I knew that 30-50% of that were basically heating the PSU (which was proprietary of course, and not easy to swap).

Good luck with your project, sounds like you've decided to go ahead with it.

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